${{\mathit \eta}^{\,'}{(958)}}$ $\rightarrow$ ${{\mathit \eta}}{{\mathit \pi}}{{\mathit \pi}}$ DECAY PARAMETERS
$\vert $MATRIX ELEMENT$\vert ^2$ ${}\propto$ 1 + $\mathit a~Y$ + $\mathit b~Y{}^{2}$ + $\mathit c~X$ + $\mathit d~X{}^{2}$

$\mathit X$ and $\mathit Y$ are Dalitz variables and $\mathit a,~b,~c$, and $\mathit d$ are real-valued parameters. May be different for ${{\mathit \eta}^{\,'}{(958)}}$ $\rightarrow$ ${{\mathit \eta}}{{\mathit \pi}^{+}}{{\mathit \pi}^{-}}$ and ${{\mathit \eta}^{\,'}{(958)}}$ $\rightarrow$ ${{\mathit \eta}}{{\mathit \pi}^{0}}{{\mathit \pi}^{0}}$ decays. We do not average measurements in the section below because parameter values from each experiment are strongly correlated.

$\mathit b$ decay parameter

INSPIRE   PDGID:
M002DPB
VALUE EVTS DOCUMENT ID TECN  COMMENT
• • We do not use the following data for averages, fits, limits, etc. • •
$-0.066$ $\pm0.006$ $\pm0.001$ 1
ABLIKIM
2023AH
 BES3 ${{\mathit \eta}^{\,'}}$ $\rightarrow$ ${{\mathit \eta}}{{\mathit \pi}^{0}}{{\mathit \pi}^{0}}$
$-0.049$ $\pm0.006$ $\pm0.006$ 351k
ABLIKIM
2018
BES3 ${{\mathit \eta}^{\,'}}$ $\rightarrow$ ${{\mathit \eta}}{{\mathit \pi}^{+}}{{\mathit \pi}^{-}}$
$-0.073$ $\pm0.014$ $\pm0.005$ 56k
ABLIKIM
2018
BES3 ${{\mathit \eta}^{\,'}}$ $\rightarrow$ ${{\mathit \eta}}{{\mathit \pi}^{0}}{{\mathit \pi}^{0}}$
$-0.063$ $\pm0.014$ $\pm0.005$ 124k
ADLARSON
2018A
 A2MM ${{\mathit \eta}^{\,'}}$ $\rightarrow$ ${{\mathit \eta}}{{\mathit \pi}^{0}}{{\mathit \pi}^{0}}$
$-0.052$ $\pm0.001$ $\pm0.002$ 2
GONZALEZ-SOLI..
2018A
 RVUE ${{\mathit \eta}^{\,'}}$ $\rightarrow$ ${{\mathit \eta}}{{\mathit \pi}^{0}}{{\mathit \pi}^{0}}$
$-0.069$ $\pm0.019$ $\pm0.009$ 44k 3
ABLIKIM
2011
BES3 ${{\mathit J / \psi}}$ $\rightarrow$ ${{\mathit \gamma}}{{\mathit \eta}}{{\mathit \pi}^{+}}{{\mathit \pi}^{-}}$
$-0.063$ $\pm0.028$ $\pm0.004$ 15k 4
BLIK
2009
GAM4 32.5 ${{\mathit \pi}^{-}}$ ${{\mathit p}}$ $\rightarrow$ ${{\mathit \eta}^{\,'}}{{\mathit n}}$
$-0.106$ $\pm0.028$ $\pm0.014$ 20k 5
DOROFEEV
2007
VES 27 ${{\mathit \pi}^{-}}$ ${{\mathit p}}$ $\rightarrow$ ${{\mathit \eta}^{\,'}}{{\mathit n}}$, ${{\mathit \pi}^{-}}$ ${{\mathit A}}$ $\rightarrow$ ${{\mathit \eta}^{\,'}}{{\mathit \pi}^{-}}{{\mathit A}^{*}}$
1  Fit IV, ignoring noncusp terms. Supersedes ABLIKIM 2018.
2  Theoretical analysis of ADLARSON 2018A using resonance chiral perturbation theory to one loop.
3  See ABLIKIM 2011 for the full correlation matrix.
4  From ${{\mathit \eta}^{\,'}}$ $\rightarrow$ ${{\mathit \eta}}{{\mathit \pi}^{0}}{{\mathit \pi}^{0}}$ decay.
5  From ${{\mathit \eta}^{\,'}}$ $\rightarrow$ ${{\mathit \eta}}{{\mathit \pi}^{+}}{{\mathit \pi}^{-}}$ decay.
References